A deadly trade

What’s in a name? Ash fungus by any other name would have burned as sweet in the recent bonfires. But the name does make a difference. Had it not been for name-related confusion, the government might have imposed a ban on imports of ash and ash products years ago. Then the pointless, self-defeating burning could have been avoided.

EU rules prohibit a ban on imports of a species if the threatening pathogen is already endemic. The ash fungus is widely reported as being Chalara fraxinea. This is widespread in the UK, and benign: no ban was possible. However, many fungi exist in two forms, one that reproduces sexually, and one that reproduces asexually. In 2009, researchers suggested that the pathogen was in fact Hymenoscyphus albidus, a sexually reproducing version of Chalara fraxinea. A ban, then, was still impossible. But last year Swiss researchers showed the pathogen to be a different organism that they named Hymenoscyphus pseudo-albidus. That could have been banned.

Things could get worse. A decision taken at the International Botanical Congress in Melbourne last year means that mycologists – those who study fungi – will no longer be allowed to give separate names to the sexually and asexually reproducing variants of a species. Ironically, the idea is to limit confusion. With all the evolving variations of our forest pathogens, it’s likely to cause more problems than it solves.

Evolution is fearsome to behold. We’ve been watching it in our hospitals for years – it is what gave us our antibiotic-resistant superbugs. Put a wide variety of bacteria together in a confined space with plenty of very habitable niches and they will indulge in an orgy of gene-swapping. This creates new strains, many of which are resistant to all known toxins.

Ash dieback is another example of an evolved pathogen. It arose in Poland in 1992. There is nothing we can do about it except let the naturally resistant trees emerge as winners in the evolutionary arms race. It’s impossible to tell which trees will survive without carrying out a genetic analysis; that’s why burning swaths of ash trees is self-defeating.

In truth, the issue over naming the fungus is probably a convenient scapegoat. Researchers were advising an import ban years before anyone looked into whether the fungus was of an endemic species. Somehow, no one wanted to react to the threat, and it’s not just the UK’s researchers who didn’t want to see the coming evil: Danish experts pointed out an impending problem to the Swedes, and they did nothing either.

Import duty

What we can do now to safeguard the future of our forests is reduce the demand for imported plants. Read the scientific literature on plant pathogens, and you find that experts are issuing 13 times as many alerts on new plant-infecting fungi as they were in 1995. The ash fungus may be one of the relatively few natural mutations that have occurred in recent times: most of them are triggered by human activities. Plant pathologists put the blame squarely on the taste for imported plants.

Our craving for exotic plants and ready-grown trees for our gardens and public spaces has moved plants and their pathogens around the world in unprecedented numbers. In new environments, the pathogens swap genes and evolve into forms for which native species have no resistance.

The surging global trade in plants is essentially a huge microbiology experiment that is destroying the world’s forests. But perhaps we think that interesting suburban gardens are worth it?

Michael Brooks’s “The Secret Anarchy of Science” is published by Profile Books (£8.99)

Michael Brooks holds a PhD in quantum physics. He writes a weekly science column for the New Statesman, and his most recent book is At The Edge of Uncertainty: 11 Discoveries Taking Science By Surprise.